A cotton fiber-based nitrogen-doped carbon material, its preparation method and application

Abstract

This invention belongs to the field of pollutant treatment technology, specifically disclosing a method for preparing cotton fiber-based nitrogen-doped carbon materials. First, cotton fibers are washed and then treated with an alkaline bath, a nitrogen-containing organic solvent for swelling, and glycerol / liquid ammonia to obtain cotton cellulose I, cotton cellulose II, cotton cellulose III, and cotton cellulose IV. A nitrogen source is dispersed in an aqueous solution, and then cotton fibers are added, soaked, and freeze-dried to obtain a cotton cellulose-nitrogen source precursor. The cotton cellulose-nitrogen source precursor is then pyrolyzed under an inert atmosphere to obtain the cotton fiber-based nitrogen-doped carbon material. Using cotton fibers as the carbon source, the self-assembled complex of cotton fibers and the nitrogen source is pyrolyzed, increasing the active nitrogen component in the catalyst and improving catalytic degradation performance. When waste cotton is used as the raw material, it not only achieves the effect of degrading dye pollutants but also achieves the goal of high-value recycling of waste cotton fibers.

Description

Technical Field

[0001] This invention belongs to the field of pollutant treatment technology, specifically relating to a cotton fiber-based nitrogen-doped carbon material, its preparation method, and its application. Background Technology

[0002] The problem of textile dyeing and printing wastewater is currently very serious. According to incomplete statistics, the daily discharge of textile dyeing and printing wastewater in my country is approximately 3 × 10⁻⁶. 6 ~4×10 6 m 3 This accounts for approximately 35% of the total industrial wastewater discharge. Currently, the utilization rate of reactive dyes, which are widely used in the dyeing and printing industry, is only 60-70%. For every 100 meters of fabric processed, a dyeing and printing plant generates 3-5 meters of wastewater. 3 Wastewater has become one of the most polluting and harmful pollutants in the dyeing and printing industry. The degradation of organic pollutants in dye wastewater is an important direction for wastewater treatment. Novel advanced oxidation technologies based on persulfate have advantages such as high stability, good solubility, wide applicable pH range, and long lifetime of the generated sulfate free radicals, making them more conducive to the degradation of high-concentration organic pollutants. However, persulfate is relatively stable at room temperature and requires activation through heating, chelation or non-chelation of transition metal ions, light, alkali, and carbon materials such as activated carbon to generate highly oxidizing sulfate and hydroxyl free radicals, thereby efficiently and rapidly removing the target pollutants. Currently known activation methods for persulfate include the following:

[0003] 1. Thermally activated persulfate: This method involves increasing the energy of the reaction system through thermal radiation to accelerate the formation of ·OH from persulfate. - And SO4 - Free radicals can degrade dye wastewater, but this method has high thermal activation costs and low thermal utilization efficiency. Therefore, using new energy sources or improving thermal utilization efficiency are the problems faced by thermally activated persulfate.

[0004] 2. Photoactivated persulfate refers to persulfate that is activated under strong visible or ultraviolet light, producing SO4· ... - This process degrades the wastewater in the dye to achieve the desired effect. However, due to the difficulty in controlling ultraviolet light and its poor transmittance, it is difficult to obtain ideal results in industrial wastewater treatment.

[0005] 3. Ultrasonic activation of persulfate oxidation for water pollution treatment: Persulfate is added to a reaction vessel containing wastewater, mixed and dissolved, and then placed in an ultrasonic generator. The ultrasonic waves are then turned on, and after a full reaction, purified wastewater is obtained. This method is relatively novel, but difficult to implement due to its demanding conditions and low degradation efficiency, thus limiting its widespread application.

[0006] 4. Transition metal activated persulfate (TMP) effectively degrades organic pollutants by activating persulfate with chelated or non-chelated transition metal ions, such as iron and cobalt ions. This is because the suitable concentration of Fe is [missing information]. 3+ It can accelerate electron transfer to generate SO4· - and ·OH - However, although this technology can degrade dye wastewater, metal activation introduces a large amount of metal salts, which can cause secondary pollution.

[0007] 5. Carbon-based catalysts activate persulfate. Carbon materials, as a novel heterogeneous persulfate catalyst, possess characteristics such as being metal-free, having high utilization rate, being acid and alkali resistant, having ultra-high pore volume, and having a large specific surface area, making them highly promising for applications. Doping carbon materials with heteroatoms (N, S, B, or P) can significantly improve the catalytic activity of persulfate in removing organic pollutants, because these heteroatoms can introduce more active centers, promote electron transfer, and increase defects. More importantly, significant synergistic effects can occur among the components of these heteroatom-containing carbon materials to enhance catalytic activity.

[0008] Therefore, with current technology, activating persulfate with carbon-based catalysts is a relatively good approach, especially heteroatom-doped carbon materials. These materials offer fast reaction rates, wide applicability, strong removal capabilities, and can produce various highly reactive substances, including SO4· - ·OH - Superoxide radicals (O2· - ) and singlet oxygen ( 1 O2 and other nitrogen atoms can provide more options for the effective degradation of pollutants in complex dye wastewater. Nitrogen is a widely used heteroatom, and nitrogen doping can significantly improve the removal efficiency of pollutants and shorten the reaction time in almost all carbon materials with poor catalytic activity. However, such catalysts are mostly in powder form, which presents problems such as difficulty in recovery and easy secondary pollution. Summary of the Invention

[0009] The purpose of this invention is to provide a cotton fiber-based nitrogen-doped carbon material, its preparation method, and its application, which solves the problems of powdered nitrogen-carbon materials being difficult to recycle and prone to secondary pollution.

[0010] This invention is achieved through the following technical solution:

[0011] A method for preparing a cotton fiber-based nitrogen-doped carbon material includes the following steps:

[0012] (1) Tear the recycled waste cotton fibers into pieces, wash and dry them to obtain raw cotton fibers for later use.

[0013] (2) Soak the raw cotton fibers in an alkaline solution, treat them in a water bath, then wash them with deionized water until neutral and dry them to obtain cotton cellulose I;

[0014] Cotton cellulose I was soaked in an alkaline solution, washed with deionized water until neutral, and then dried to obtain cotton cellulose II;

[0015] Cotton cellulose I was soaked in a nitrogen-containing organic solvent, and the sample was repeatedly washed with methanol until the solvent was completely removed. After drying, cotton cellulose III was obtained.

[0016] Cotton cellulose III was heated in glycerol or liquid ammonia, and the resulting sample was washed with deionized water and acetone until the solvent was completely removed. The sample was then dried to obtain cotton cellulose IV.

[0017] (3) Disperse the nitrogen source in an aqueous solution, then add one or more of cotton cellulose I, cotton cellulose II, cotton cellulose III, and cotton cellulose IV, sonicate at room temperature, freeze dry to obtain cotton cellulose-nitrogen source precursor;

[0018] (4) Pyrolyze the cotton cellulose-nitrogen source precursor under an inert atmosphere at a temperature of 300-1000℃ to obtain cotton fiber-based nitrogen-doped carbon material.

[0019] The nitrogen-carbon atom ratio in the cotton fiber-based nitrogen-doped carbon material is (0.10 to 0.41):1.

[0020] Furthermore, in step (2), when preparing cotton cellulose I, the raw cotton fibers are soaked in an alkaline solution at a bath solution ratio of 1:50;

[0021] When preparing cotton cellulose II, cotton cellulose I was soaked in an alkaline solution at a bath-liquid ratio of 1:100.

[0022] In the preparation of cotton cellulose III, cotton cellulose I was soaked in a nitrogen-containing organic solvent at a bath-to-solution ratio of 1:100 to swell.

[0023] When preparing cotton cellulose IV, cotton cellulose III is placed in glycerol or liquid ammonia and heated at a bath ratio of 1:100.

[0024] Furthermore, in the preparation of cotton cellulose II, the alkaline solution is a NaOH solution with a mass concentration of 10-20%, the soaking time is 1-2 hours, and the drying method is hot drying or freeze drying.

[0025] Furthermore, when preparing cotton cellulose III, the swelling time is 15 min to 24 h, and the nitrogen-containing organic solvent is ethylenediamine, liquid ammonia, or ammonia water.

[0026] Furthermore, when preparing cotton cellulose IV, the heating temperature is 140–260℃, the holding time is 0.5–64 h, and the drying method is hot drying or freeze drying.

[0027] Furthermore, in step (3), the nitrogen source is one or more of urea, dicyandiamide, melamine and polyaniline.

[0028] Furthermore, in step (3), the concentration of the nitrogen source dispersion is 3% to 20%.

[0029] Furthermore, in step (4), the inert gas used during pyrolysis is nitrogen, argon or helium, and the pyrolysis time is 1-3 hours.

[0030] The cotton fiber-based nitrogen-doped carbon material prepared by the preparation method described in this invention.

[0031] The present invention also discloses the application of the cotton fiber-based nitrogen-doped carbon material as a catalyst for activating persulfate. When the cotton fiber-based nitrogen-doped carbon material activates persulfate, it generates sulfate free radicals.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material. Using cotton fiber as the carbon source, the method involves pyrolyzing a self-assembled composite of a nitrogen source and cotton cellulose. The prepared cotton fiber-based nitrogen-doped carbon material contains a high nitrogen-to-carbon atomic ratio (0.10–0.41). The high nitrogen content can increase the active nitrogen component in the catalyst, which is beneficial to improving the catalytic degradation performance. The nitrogen-doped carbon materials prepared from different crystalline forms of cotton cellulose have different graphite-to-carbon ratios. A high graphite-to-carbon content is beneficial to improving the electron transfer ability of the material, giving the catalyst good electrical conductivity. On the other hand, it allows nitrogen atoms in the nitrogen source to enter the carbon layer of the cotton fiber through atomic thermal motion, forming an active component with persulfate catalytic activity.

[0034] The preparation process of this invention is environmentally friendly and safe, with a simple process and low cost; it does not use sacrificial elements or precious metals, belonging to an atom-economical preparation method. Furthermore, the prepared cotton fiber-based nitrogen-doped carbon material, using cotton fiber as a carrier, retains some of the cotton fiber's appearance after pyrolysis, facilitating catalyst recycling and achieving sustainable resource development.

[0035] This invention proposes to use cotton fiber, after treatment, as a carbon source and carrier for metal nitrogen-doped carbon materials that activate persulfate. This not only solves the problem of the difficulty in recycling powdered nitrogen-carbon materials, but also combines the dye adsorption process with the advanced oxidation degradation process, reducing the regeneration problem of adsorption materials. This provides a new approach to practically solve the real problem of wastewater in the printing and dyeing industry and achieve the goal of "treating waste with waste".

[0036] Furthermore, when the cotton fiber is sourced from waste cotton fibers, the cost can be significantly reduced.

[0037] This invention also discloses a cotton fiber-based nitrogen-doped carbon material prepared by the above preparation method and its application. The material has good catalytic activity and stability and can be used to degrade persulfate to treat wastewater. This heterogeneous catalyst can be used at room temperature and away from light. It has a wide range of applications and has the advantages of high catalytic efficiency, strong oxidation ability, easy recovery and good reusability. It has great application prospects in the treatment of organic polluted water bodies in the fields of groundwater and printing and dyeing. Attached Figure Description

[0038] Figure 1 The XRD pattern of cotton cellulose III prepared in Example 1;

[0039] Figure 2 SEM image of the cotton fiber-based nitrogen-carbon material prepared in Example 1;

[0040] Figure 3 The XRD pattern of cotton cellulose II prepared in Example 2;

[0041] Figure 4 This is a SEM image of the cotton fiber-based nitrogen-carbon material prepared in Example 2;

[0042] Figure 5 The XRD pattern of cotton cellulose I prepared in Example 3;

[0043] Figure 6 XPS spectrum of nitrogen element in cotton fiber-based nitrogen-carbon material prepared in Example 3;

[0044] Figure 7 The XRD pattern of cotton cellulose IV prepared in Example 4;

[0045] Figure 8 The NLDFT pore size distribution diagram of the cotton fiber-based nitrogen-carbon material prepared in Example 4 is shown.

[0046] Figure 9 The XRD pattern of cotton cellulose III prepared in Example 5;

[0047] Figure 10 The XRD pattern of cotton cellulose IV prepared in Example 6;

[0048] Figure 11 The nitrogen adsorption-desorption curves for the cotton fiber-based nitrogen-carbon material prepared in Example 6 are shown.

[0049] Figure 12 XPS spectrum of nitrogen element in cotton fiber-based nitrogen-carbon material prepared in Example 7;

[0050] Figure 13 A comparison of the XRD spectra of the cotton fiber-based nitrogen-carbon materials prepared in Examples 6 and 7;

[0051] Figure 14 A comparative graph showing the time-degradation efficiency relationship when cotton fiber-based nitrogen-carbon materials prepared in Comparative Example 1 and Examples 1, 3, 4, and 6 are activated to degrade Reactive Blue 19 dye liquor by persulfate.

[0052] Figure 15 The electron paramagnetic resonance spectrum of the cotton fiber-based nitrogen-carbon material and the 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO) system of the present invention after adding potassium persulfate for 10 minutes is shown. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0054] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0055] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0056] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0057] Example 1

[0058] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0059] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0060] (2) Soak cotton cellulose I in a mixed solution of 75:25 (v:v) ethylenediamine and water with a bath ratio of 1:100. After swelling for 24 hours, wash the sample repeatedly with a large amount of methanol until the ethylenediamine is completely removed. Dry the sample to obtain cotton cellulose III.

[0061] (3) Disperse urea in 30 mL of aqueous solution to obtain a 15% urea solution, then add 0.5 g of cotton cellulose III, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose III-urea precursor.

[0062] (4) The cotton cellulose III-urea precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Argon gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 500 °C and kept at 1 hour for natural cooling to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as C-III-15Urea-500.

[0063] Figure 1 The XRD pattern of the prepared cotton cellulose III is shown. The characteristic diffraction peaks at 11.6°, 17.1°, 20.5°, 20.9°, 28.4°, 34.7°, 40.4°, and 44.3° correspond to the (010), (002), (100) / (012), (1-10), (013), (004), (2-10), and (123) crystal planes of cellulose IIII, respectively, indicating that this method can prepare cotton cellulose III with high crystallinity. Figure 2 The SEM image of cotton fiber-based nitrogen-doped carbon material C-III-15Urea-500 reveals a flocculent nanolayer adhering to the surface of the cotton fibers, indicating that it is a nitrogen-doped carbon material resulting from the carbonization of the urea / cotton composite. XPS analysis shows that the cotton fiber-based nitrogen-doped carbon material contains 79.9% (at) C, 17.6% (at) N, and 2.5% (at) O, resulting in a nitrogen-to-carbon ratio of 0.22. This high nitrogen-to-carbon ratio enhances the material's electron transfer capability, leading to good conductivity in the catalyst.

[0064] Example 2

[0065] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0066] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0067] (2) Soak cotton cellulose I in a 18.5% NaOH solution at a bath ratio of 1:100 for 1.5 h, wash with a large amount of deionized water until neutral, and then freeze dry for 12 h to obtain cotton cellulose II.

[0068] (3) Disperse melamine in 30 mL of aqueous solution to obtain a 3% melamine solution, then add 0.5 g of cotton cellulose II, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose II-melamine precursor.

[0069] (4) The cotton cellulose II-melamine precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Argon gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 600 °C and kept at 600 °C for 2 hours before being cooled naturally to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as C-II-3Melamine-600.

[0070] Figure 3 The XRD pattern of the prepared cotton cellulose II is shown. The characteristic diffraction peaks at 12.0°, 19.8°, 20.4°, 22.0°, 28.8°, 34.9°, 36.6°, 40.9°, and 46.0° correspond to the (1-10), (110), (012), (020), (013), (004), (014), (130), and (105) crystal planes of cellulose II, respectively. Figure 4 The SEM image of cotton fiber-based nitrogen-doped carbon material C-II-3 Melamine-600 shows that a flocculent nanolayer is also attached to the surface of the cotton fiber, indicating that it is a nitrogen-doped carbon material after carbonization of the melamine / cotton composite. However, the amount of flocculent material attached is less than that of C-III-15 Urea-500 prepared in Example 1, therefore its catalytic performance is also lower than that of Example 1. XPS tests show that the C content in the cotton fiber-based nitrogen-doped carbon material is 83.0 (at)%, the N content is 9.8 (at)%, and the O content is 7.2 (at)%, meaning that the nitrogen-carbon ratio of the cotton fiber-based nitrogen-doped carbon material is 0.12.

[0071] Example 3

[0072] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0073] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0074] (2) Disperse dicyandiamide in 30 mL of aqueous solution to obtain a 5% dicyandiamide solution, then add 0.5 g of cotton cellulose I, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose I-dicyandiamide precursor.

[0075] (3) The cotton cellulose I-dicyandiamide precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Nitrogen gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 800 °C and kept at 800 °C for 2 hours before being cooled naturally to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as CI-5DCD-800.

[0076] Figure 5 The XRD pattern of the prepared cotton cellulose I is shown. The characteristic diffraction peaks at 14.8°, 16.6°, 20.6°, 22.8°, 27.9°, 34.4°, 41.8°, and 45.0° correspond to the (1-10), (110), (102), (200), (013), (004), (204), and (105) crystal planes of cellulose I, respectively. Figure 6 As shown in the XPS spectrum of nitrogen element in the cotton fiber-based nitrogen-doped carbon material, the main nitrogen types are pyridine nitrogen, graphitic nitrogen, pyrrole nitrogen, and nitrogen oxides. Pyridine nitrogen and pyrrole nitrogen have relatively high atomic contents in the material, and these two types of nitrogen are considered to be active nitrogen. Furthermore, XPS testing revealed that the C content in the cotton fiber-based nitrogen-doped carbon material is 83.2 (at)%, the N content is 10.4 (at)%, and the O content is 6.4 (at)%, resulting in a nitrogen-to-carbon ratio of 0.13. Perhaps due to the relatively low total nitrogen content, the degradation rate of CI-5DCD-800 in Table 1 is not high (55% at 40 min).

[0077] Example 4

[0078] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0079] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0080] (2) Cotton cellulose III was placed in glycerol at a bath ratio of 1:100, and then heated in a high-pressure reactor at 260°C for 30 min. The obtained sample was treated with a large amount of deionized water and acetone until the glycerol was completely removed, and then freeze-dried to obtain cotton cellulose IV.

[0081] (3) Disperse urea in 30 mL of aqueous solution to obtain a 10% urea solution, then add 0.5 g of cotton cellulose IV, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose IV-urea precursor.

[0082] (4) The cotton cellulose IV-urea precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Nitrogen gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 700 °C and kept at 700 °C for 1 hour before being allowed to cool down naturally to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as C-IV-10Urea-700.

[0083] Figure 7 The XRD pattern of the prepared cotton cellulose IV is shown. The characteristic diffraction peaks at 13.8°, 15.5°, 20.5°, 22.2°, 28.2°, and 34.6° correspond to the (011) / (10-1), (1-10), (102), (200), (103), and (004) crystal planes of cellulose IV, respectively, indicating that the method successfully prepared cotton cellulose IV. Figure 8 The image shows the NLDFT pore size distribution of the cotton fiber-based nitrogen-doped carbon material. It can be seen that the pore size in the C-IV-10Urea-700 material is concentrated between 2-10 nm, and the higher micropore size provides more active sites. Based on nitrogen physisorption tests, the BET specific surface area of ​​the C-IV-10Urea-700 material is 117.9 m². 2 The / g indicates that the cotton fiber-based nitrogen-carbon material prepared in this embodiment has a high specific surface area. A large specific surface area is beneficial for mass transfer and exposure of active sites during the catalytic activation of PMS. According to XPS tests, the C content in the cotton fiber-based nitrogen-doped carbon material is 80.4 (at)%, the N content is 14.1 (at)%, and the O content is 5.5 (at)%, that is, the nitrogen-carbon ratio of the cotton fiber-based nitrogen-doped carbon material is 0.18.

[0084] Example 5

[0085] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0086] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0087] (2) Soak cotton cellulose I in liquid ammonia at a ratio of 1:100. After swelling for 15 minutes, wash the sample repeatedly with a large amount of methanol until the liquid ammonia is completely removed. Dry the sample to obtain cotton cellulose III.

[0088] (3) Disperse melamine in 30 mL of aqueous solution to obtain a 5% melamine solution, then add 0.5 g of cotton cellulose III, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose III-melamine precursor.

[0089] (4) The cotton cellulose III-melamine precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Helium gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 900 °C and kept at 900 °C for 1 hour before being allowed to cool down naturally to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as C-III-5Melamine-900.

[0090] Figure 9 The XRD pattern of the prepared cotton cellulose III is shown. The characteristic diffraction peaks at 11.6°, 17.1°, 20.5°, 20.9°, 28.4°, and 34.7° correspond to the (010), (002), (100) / (012), (1-10), (013), and (004) crystal planes of cellulose III, respectively. The relative peak intensity of the (100) / (012) crystal plane is higher than that of the cellulose III prepared in Example 1, indicating that the cotton cellulose III obtained by different preparation methods is slightly different. In addition, XPS tests showed that the C content in the cotton fiber-based nitrogen-doped carbon material was 82.3 (at)%, the N content was 11.3 (at)%, and the O content was 6.4 (at)%, that is, the nitrogen-carbon ratio of the cotton fiber-based nitrogen-doped carbon material was 0.14. The higher nitrogen-carbon ratio is beneficial to improving the electron transfer ability of the material, giving the catalyst good conductivity.

[0091] Example 6

[0092] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0093] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0094] (2) Place the cotton cellulose III in liquid ammonia according to a bath ratio of 1:100, then heat it in a high-pressure reactor at 140 °C for 1 h. Wash the obtained sample with a large amount of deionized water and acetone until the liquid ammonia is completely removed, and then vacuum heat-dry it to obtain cotton cellulose IV.

[0095] (3) Disperse dicyandiamide in 30 mL of aqueous solution to obtain a 15% dicyandiamide solution. Then add 0.5 g of cotton cellulose IV and soak it in an ultrasonic bath at room temperature for 12 h. After freeze-drying, a cotton cellulose IV-dicyandiamide precursor is obtained.

[0096] (4) Pyrolyze the cotton cellulose IV-dicyandiamide precursor in a quartz boat of a tubular furnace, introduce helium with a flow rate of 80 mL / min, and the heating rate is 5 °C per minute. Carbonize and pyrolyze at 500 °C and keep it for 2 h, then naturally cool down to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as C-IV-15Urea-500.

[0097] Figure 10 The XRD pattern of the prepared cotton cellulose IV is shown. The characteristic diffraction peaks at 13.8°, 15.5°, 20.5°, 22.2°, 28.2°, and 34.6° correspond to the (011) / (10-1), (1-10), (102), (200), (103), and (004) crystal planes of cellulose IV respectively. The peaks of the (011) / (10-1) and (1-10) crystal planes are weaker than the relative peak intensities of the cellulose IV prepared in Example 4, indicating that the cotton cellulose IV obtained by different preparation methods is slightly different. Figure 11 The nitrogen adsorption and desorption curve of the cotton fiber-based nitrogen-doped carbon material is shown. It can be seen that the adsorption and desorption curve of C-IV-15Urea-500 has a typical Type IV isotherm and there is a H4-type hysteresis loop in the region of 0.4 < P / P0 < 1.0, indicating that the composite material has a mesoporous structure. According to the nitrogen physical adsorption test, the BET specific surface area of the C-IV-10Urea-700 material is 113.7 m 2 / g, indicating that the specific surface area of the cotton fiber-based nitrogen-carbon material prepared in this example is lower than that of the cotton fiber-based nitrogen-carbon material prepared in Example 4. According to the XPS test, the C content in the cotton fiber-based nitrogen-doped carbon material is 82.3 (at)%, the N content is 15.6 (at)%, and the O content is 2.1 (at)%, that is, the nitrogen-carbon element content ratio of the cotton fiber-based nitrogen-doped carbon material is 0.19.

[0098] Example 7

[0099] The present invention discloses a preparation method of a cotton fiber-based nitrogen-doped carbon material, which includes the following steps:

[0100] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0101] (2) Disperse urea in 30 mL of aqueous solution to obtain a 20% urea solution, then add 0.5 g of cotton cellulose I, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose I-urea precursor.

[0102] (3) The cotton cellulose I-urea precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Argon gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 600 °C and kept at 600 °C for 2 hours before being cooled naturally to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as CI-20Urea-600.

[0103] XPS analysis revealed that the cotton fiber-based nitrogen-doped carbon material contained 66.7 (at)% C, 27.2 (at)% N, and 0.5 (at)% O, resulting in a nitrogen-to-carbon ratio of 0.41. This relatively high nitrogen-to-carbon ratio enhances the material's electron transfer capability, leading to good electrical conductivity. The XPS spectrum of the nitrogen element in the cotton fiber-based nitrogen-doped carbon material is also shown. Figure 12 As can be seen from the table, the main nitrogen types in CI-20Urea-600 material are pyridine nitrogen, graphitic nitrogen, pyrrole nitrogen and nitrogen oxides, among which pyridine nitrogen has a higher content, which explains why CI-20Urea-600 has a high degradation rate (up to 97% in 40 min) as shown in Table 1.

[0104] Figure 13 A comparison of the XRD spectra of the cotton fiber-based nitrogen-carbon materials prepared in Examples 6 and 7 shows that, when different crystalline cotton fibers are used as carbon source materials, the prepared cotton fiber-based nitrogen-carbon materials exhibit two characteristic peaks at 25.1° and 42.5°, corresponding to the (002) and (100) crystal planes of the graphite structure, respectively. However, the C-IV-10Urea-700 material prepared from cotton fiber IV in Example 6 has a higher graphite peak intensity, indicating a higher degree of graphitization. It is generally believed in the industry that nitrogen-doped carbon catalysts with a high degree of graphitization are more conducive to electron transfer during PMS activation.

[0105] Example 8

[0106] This invention discloses a method for preparing a cotton fiber-based nitrogen-doped carbon material, comprising the following steps:

[0107] (1) Tear the waste cotton fibers recovered from the textile factory into small pieces, wash them with soap more than 3 times, then clean them with a large amount of deionized water to remove the residual soap and keep them visually clean. Dry them at 60°C for 12 hours to obtain raw cotton fibers for later use.

[0108] (2) Soak cotton cellulose I in a mixed solution of 75:25 (v:v) ethylenediamine and water with a bath ratio of 1:100. After swelling for 24 hours, wash the sample repeatedly with a large amount of methanol until the ethylenediamine is completely removed to obtain cotton cellulose III.

[0109] (3) Disperse polyaniline in 30 mL of aqueous solution to obtain a 3% polyaniline solution, then add 0.5 g of cotton cellulose III, sonicate for 12 h at room temperature, and freeze dry to obtain cotton cellulose III-polyaniline precursor.

[0110] (4) The cotton cellulose III-polyaniline precursor was placed in a quartz boat in a tubular furnace for pyrolysis. Nitrogen gas was introduced at a flow rate of 80 mL / min and the heating rate was 5 °C per minute. The precursor was carbonized and pyrolyzed at 800 °C and kept at 800 °C for 1 hour before being allowed to cool down naturally to obtain a cotton fiber-based nitrogen-doped carbon material, denoted as C-III-3PANI-800.

[0111] XPS testing revealed that the cotton fiber-based nitrogen-doped carbon material contained 89.1% (at) C, 8.9% (at) N, and 2.1% (at) O, meaning the nitrogen-to-carbon ratio of the catalyst material was 0.10.

[0112] Comparative Example 1

[0113] 0.5g of cotton cellulose III was directly placed in a quartz boat in a tubular furnace for pyrolysis (i.e., without adding a nitrogen source), argon gas was introduced at a flow rate of 80mL / min, the temperature was increased at a rate of 5℃ per minute, and the temperature was maintained at 500℃ for 2 hours before being allowed to cool naturally to obtain the C-III-500 catalyst.

[0114] Comparative Example 2

[0115] 0.5g of melamine was directly placed in a quartz boat in a tubular furnace for pyrolysis (i.e., without adding a carbon source), and argon gas was introduced at a flow rate of 80mL / min. The temperature was increased by 5℃ per minute and held at 500℃ for 2 hours before being allowed to cool naturally to obtain the C-Melamine-500 catalyst.

[0116] A comparative study was conducted on the application of the materials prepared in Example 1, Comparative Examples 1 and 2 in the oxidative degradation of Reactive Blue 19 by activated bisulfate, including the following steps:

[0117] Prepare three groups of Reactive Blue 19 solutions with a concentration of 20 mg / L and a volume of 120 mL. Add 36 mg of CC-MIL-10DCD-1000 from Example 1, CC-MIL-0DCD-1000 from Comparative Example 2, and NCC-MIL-10DCD-1000 from Comparative Example 3 to the three groups respectively. Stir for one hour in the dark to allow adsorption equilibrium to be reached. Then add 0.22 g (3 mM) of potassium persulfate to the third group of Reactive Blue 19 solutions. After the reaction is complete, the degradation of Reactive Blue 19 is finished.

[0118] Determination of degradation efficiency: Every 5 minutes, 2 mL of reaction solution was taken from each reaction solution and added to a centrifuge tube containing an equal volume of 2 mL of methanol quencher. The absorbance of the solution was then measured on a UV-Vis spectrophotometer. The actual concentration was twice the measured concentration of the dye solution.

[0119] Table 1. Effects of Examples and Comparative Examples on the Degradation of Reactive Blue 19 by Activated Persulfate Degradation

[0120]

[0121] The above experiments compared the effects of adding nitrogen and carbon sources on the degradation of Reactive Blue 19 dye by a cotton fiber-based nitrogen-doped carbon material catalyst.

[0122] Experiments show that, compared with the C-III-500 prepared in Comparative Example 1, the C-III-15Urea-500 catalyst prepared in Example 1 may have generated active nitrogen components after the addition of a nitrogen source, which greatly improves the activation effect on persulfate and effectively promotes the generation of sulfate radicals and hydroxyl radicals from persulfate to oxidize and degrade Reactive Blue 19, thus significantly improving the degradation effect of Reactive Blue 19.

[0123] like Figure 14 As shown, it can be seen that the degradation performance of Comparative Example 1 and the blank control is significantly reduced compared to the dye degradation performance of the catalysts corresponding to Examples 1, 3, 4 and 6. Among them, Comparative Example 1 is the product of carbonized cotton fiber III only, which indicates that the nitrogen source and cotton fiber play an important role in the formation of persulfate catalytic active components in cotton fiber-based nitrogen-doped carbon materials.

[0124] like Figure 15 As shown, after adding potassium persulfate for 10 minutes, the reactive oxygen free radicals SO4·2O3 generated by the cotton fiber-based nitrogen-doped carbon material... - and ·OH - The presence of SO4·4·5-dimethyl-1-pyrrolidone-N-oxide (DMPO) indicates that the cotton fiber-based nitrogen-doped carbon material prepared in this invention generates SO4· ... - and ·OH -To oxidize and degrade organic pollutants in dyes.

[0125] In summary, the persulfate catalyst prepared by this invention has excellent activation and catalytic performance, the fibrous catalyst is easy to recover and reuse, and it has good stability. Therefore, it has good application prospects in the treatment of wastewater such as dyes.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a cotton fiber-based nitrogen-doped carbon material, characterized in that, Includes the following steps: (1) Tear the recycled waste cotton fibers into pieces, wash and dry them to obtain raw cotton fibers for later use; (2) Soak the raw cotton fibers in an alkaline solution, treat them in a water bath, wash them with deionized water until neutral, and then dry them to obtain cotton cellulose I; Cotton cellulose I was soaked in a nitrogen-containing organic solvent, and the sample was repeatedly washed with methanol until the solvent was completely removed. After drying, cotton cellulose III was obtained. Cotton cellulose III was heated in glycerol or liquid ammonia, and the resulting sample was washed with deionized water and acetone until the solvent was completely removed. The sample was then dried to obtain cotton cellulose IV. (3) Disperse the nitrogen source in an aqueous solution, then add cotton cellulose III or cotton cellulose IV, sonicate and soak at room temperature, freeze dry to obtain cotton cellulose-nitrogen source precursor; in step (3), the nitrogen source is one or more of urea, dicyandiamide, melamine and polyaniline, and the mass concentration of the nitrogen source dispersion is 3%~20%; (4) The cotton cellulose-nitrogen source precursor was pyrolyzed in an inert atmosphere at a temperature of 500-900℃ to obtain cotton fiber-based nitrogen-doped carbon material. The nitrogen-to-carbon atomic ratio in the cotton fiber-based nitrogen-doped carbon material is (0.22~0.41):

1. In step (2), when preparing cotton cellulose I, the raw cotton fibers are soaked in an alkaline solution at a bath ratio of 1:50; In the preparation of cotton cellulose III, cotton cellulose I was soaked in a nitrogen-containing organic solvent at a bath-to-solution ratio of 1:100 to swell. When preparing cotton cellulose IV, cotton cellulose III is placed in glycerol or liquid ammonia and heated at a bath ratio of 1:100; When preparing cotton cellulose III, the swelling time is 15 min to 24 h, and the nitrogen-containing organic solvent is ethylenediamine; When preparing cotton cellulose IV, the heating temperature is 140~260 ℃, the holding time is 0.5~64 h, and the drying method is hot drying or freeze drying; When cotton fiber-based nitrogen-doped carbon materials are activated with persulfate, sulfate radicals are generated.

2. The method for preparing cotton fiber-based nitrogen-doped carbon material according to claim 1, characterized in that, In step (4), the inert gas used during pyrolysis is nitrogen, argon or helium, and the pyrolysis time is 1-3 hours.

3. The cotton fiber-based nitrogen-doped carbon material prepared by the preparation method described in claim 1 or 2.

4. The application of the cotton fiber-based nitrogen-doped carbon material of claim 3 as a catalyst for the activation of persulfate, characterized in that, When cotton fiber-based nitrogen-doped carbon materials are activated with persulfate, sulfate radicals are generated.

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